Photonucleon Total Cross Sections at Very High Energy

Abstract

Photon-neutron total cross sections have been evaluated from the data for the proton and deuteron presented in the preceding paper. Simple Regge-pole fits have been made to ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$ and ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}n)$, both of which extrapolate to 94 \ifmmode\pm\else\textpm\fi{} 4 \ensuremath{\mu}b at infinite energy. Over the range of our data, 3.7 to 17.9 GeV, ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}n)<{\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$, which can be interpreted to give a ratio of exchange contributions, $\frac{{A}_{2}}{{P}^{\ensuremath{'}}}=0.19\ifmmode\pm\else\textpm\fi{}0.04$. A fit to ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$ is also important for predictions of the proton cosmic-ray spectrum.